histogram_area.cpp

#include <iostream> 
#include <stack>
using namespace std;

int getMaxArea(int hist[], int n) {
  stack < int > s;

  int max_area = 0;
  int tp;
  int area_with_top;

  int i = 0;
  while (i < n) {

    if (s.empty() || hist[s.top()] <= hist[i])
      s.push(i++);

    else {
      tp = s.top();
      s.pop();

      area_with_top = hist[tp] * (s.empty() ? i : i - s.top() - 1);

      if (max_area < area_with_top)
        max_area = area_with_top;
    }
  }

  while (s.empty() == false) {
    tp = s.top();
    s.pop();
    area_with_top = hist[tp] * (s.empty() ? i : i - s.top() - 1);

    if (max_area < area_with_top)
      max_area = area_with_top;
  }

  return max_area;
}

int main() {
  int n;
  cout << "Enter the number of bars:";
  cin >> n;
  cout << endl;
  int hist[n];
  cout << "enter the heights of bars" << endl;
  for (int i = 0; i < n; i++) {
    cin >> hist[i];
  }

  cout << endl << "Maximum area is " << getMaxArea(hist, n);
  return 0;
}